The present invention relates to methods and systems for controlling or managing DC machines, and more particularly to methods and systems for limiting regenerative current of DC machines, and particularly permanent magnet DC (PMDC) machines.
Electrical power steering (EPS) systems use an electric motor as an actuator to provide assist to a driver while steering a vehicle and/or to provide vehicle control. Brushed DC machines are widely used in the Electric Power Steering (EPS) industry for low-cost applications and platforms. Electric drive systems employing such machines require fewer sensors and low-cost electronic circuitry and are able to deliver good performance through the entire operating space.
In order to protect the voltage source (e.g., a car battery) to the motor control system, a voltage versus supply current limit is typically imposed. In addition, the maximum supply current that can be supplied back to battery, i.e. regenerative current, is also limited. This may be in the form of a table calibrated offline or an online limit that is sent to the motor control system. Given this supply and regenerative current limits, the motor current command must be modified in order to ensure that the system does not draw any more current than specified at the cost of reduced torque capability, so that the voltage source is protected.